Is it permissible to sell services online, such as websites that send messages to customers or Facebook pages, on condition that the buyer promises and swears not to use them in ways that displease Allah?

Electronic service tools are neutral, and their ruling depends on the purpose for which they are used. The seller and producer are responsible for restricting the product in a way that prevents prohibited uses as much as possible, and refraining from selling to anyone they know or believe will use it for sin. However, if you do not know the true situation, or if the buyer uses it for permissible purposes, or commits to avoiding what is forbidden, then you are absolved. It is also important to pay attention to preserving the privacy of others when selling emails or Facebook likes.